Self-lubricating bearings used to provide low wear rates in a variety of high load applications must be resistant to damage, both during assembly and in service. They must tolerate dirty environments since some foreign material can often imbed in the liners of such bearings during service. They must also be resistant to a wide range of corrosive and non-corrosive fluids, including mild acids, alcohols, hydraulic oils, water, lubricating oils, detergents, and other materials. In many applications, these bearings must undergo impact and shock loads.
Bearings are currently available which feature a combination of a fibrous surface liner comprising a controlled filament wound pattern of both polytetrafluoroethylene (PTFE) and high strength fibers disposed within a thermosetting resin or other polymer. For example, it has been known to provide a thermo-setting resin bearing with a lining containing PTFE strands and other polymeric fabrics, which together adhere to the resin and provide a low coefficient of friction for minimizing wear. Reference is herein made to U.S. Pat. Nos. 2,953,418, to L. A. Runton et al.; 3,110,530, to F. Herman; and 3,130,979 to S. M. Shobert, which are hereby incorporated by reference.
It is generally known that PTFE, as it is customarily disposed on self-lubricating bearing surfaces, deteriorates as the temperature and fiber stresses increase during service. One attempt to overcome this deficiency has been to supplement the polytetrafluoroethylene fibers with graphite fibers and other materials to improve high temperature wear. Reference is herein made to U.S. Pat. No. 3,781,205, by J. Cairns et al. which is hereby incorporated by reference. Graphite fibers have been known to produce improved wear results, however this benefit is derived at the expense of high material costs which may range as high as $35.00 per pound.
Some have suggested that less expensive graphite powder and other solid lubricants in amounts up to 30 weight percent in the liner resin of composite bearings can provide beneficial wear results. See Cairns et al. However the usefulness of graphite powder in filament wound bearing liners has, up to now, not been proven.
Accordingly, a need exists for a self-lubricating bearing exhibiting longer wear life and improved heat dissipation. There is also a need for a low cost bearing exhibiting a lower coefficient of friction which can be manufactured using conventional winding equipment or an equivalent process.